To completely understand the cellular mechanisms of any hormone one must use in vitro techniques. To understand the mechanism of the hypothalamic releasing hormones the use of the in vitro pituitary is not sufficient, primarily because the anterior pituitary synthesizes and secretes six different hormones. We have been able to develop a technique whereby we can obtain an enriched population of each of the different pituitary cell types. These cells are viable and are growing in monolayer culture. With the use of immunocytochemical methods developed in our laboratory we can unequivocally identify each cell type in the population at both the light and electron microscopic level. With this system we plan to examine two specific steps in the release of the anterior pituitary hormones: 1) the role played by Ca ions and 2) the electrical interaction between the releasing hormones and the target cell receptor. Additional purification of the cells offers much promise for future studies into the biochemical parameters involved in the synthesis and release of the pituitary hormones. BIBLIOGRAPHIC REFERENCES: Moriarty, C.M. and M.P. Leuschen. Enriched Populations of Pituitary Thyrotrophs and Their Physiological Responsiveness. J. Cell Biol. 67, 295a, 1975. Presented at the 15th Annual Meeting of the American Society for Cell Biology. San Juan, Puerto Rico, November 11-14, 1975. Moriarty, C.M. Involvement of Intracellular Calcium in Hormone Secretion from the Rat Pituitary. J. Cell Biol. 70, 139a, 1976. Presented at the First International Congress on Cell Biology. September 5-10, 1976, Boston, Mass.